1. Field of the Invention
The invention relates to silicone aspartate copolymers and to a process for their preparation.
2. Description of the Related Art
To bond silicones to organic polymers is a relatively difficult problem which places high requirements on reaction management. A customary method for silicone copolymer preparation is the preparation of silicone polyethers from unsaturated polyethers and hydrogen-siloxanes by means of hydrosilylation, but these can only be carried out satisfactorily if the high requirements placed on the purity of the raw materials and establishment of narrow reaction conditions are observed. The main hindrance is the considerable incompatibility of the starting components, as a result of which the rate of reaction is considerably reduced. The expensive precious metal catalysts are a further disadvantage.
Besides this catalytic process, there are barely any synthesis methods with which hydrophobic siloxanes can be readily joined to hydrophilic organic polymers in a smooth reaction. This is most likely possible still with the addition of acetoacetate polyethers or acrylate polyethers onto aminosiloxanes. In both cases, the reaction times are very long on account of the low solubility of the raw materials in one another.
U.S. Pat. No. 6,664,342 B1 describes the addition of neutral maleic diesters onto aminosiloxanes. These maleic diesters are esters with C1-C4-alcohols which dissolve in the siloxane to give a clear solution and are therefore homogeneously dispersed in the siloxane. Nevertheless, reaction times of 1 to 10 hours at 80 to 220° C. are required. Moreover, the required excess of diester has to be distilled off when the reaction is complete. Aspartic ester-functional silicones are obtained; copolymers are not obtained in this way.
Although U.S. Pat. No. 5,990,334 A describes siloxanes which contain acid groups and which are obtained by the addition of acidic organic compounds which contain double bonds onto aminosiloxanes, the C═C double bonds are defined as acrylates which contain the acid group in the carbinol moiety. Such starting materials are complex to prepare and have to be protected against intrinsic polymerization with stabilizers.
EP 324 595 B1 describes the use of monomeric maleic monoesters onto which amino compounds are added. However, the amines are monomeric organic compounds with primary or secondary amine groups which dissolve homogeneously in the monomeric monoesters. The monomeric organic starting materials used in this process are compatible with one another since they contain no silicone constituent. Silicone copolymers can therefore not be obtained in this way.